The purpose of this study is to compare glucose control, quality of life and number of hypoglycemias in preschool children before and after using a real-time glucosensor. Nocturnal hypoglycemia can be missed even when the parents check their children's blood glucose several times at night. The investigators hypothesise that nocturnal hypoglycemia can be prevented by using the sensor in this age group. As a consequence, quality of life of the families will improve. The investigators also hypothesise that diabetes control will improve at 3-6 months from the beginning of the study.